Arc rated clothing depends on the system fault current and fault clearing time. Voltage alone does not allow for any of the existing (consensus) guidelines to provide a determination of the rating of protective gear. Many companies just opt for a highest rated arc rated flash-suit, however, we have found this to be infeasible from an ergonomic standpoint and also from a financial standpoint. It is often cheaper to perform an arc flash study and have expert guidance on matching the arc rated protective apparel to the arc flash hazard.
The easiest start would be to use the NFPA 70E tables. These, however, require knowledge of the system fault current and the protection clearing times. If you have an electrical engineer on site, they should be able to estimate these based on transformer sizes, cable losses, and protection operating curves. If not, then you would be best using a consultant. The benefit with a consultant is their experience and ability to guide you on the appropriate clothing. It is possible, having a 4,160V system, that motor contributions and other transients factor into the equation.
Make sure to check trade references when using consultants, we have noted an uptick on so called "experts"!